Immedediately, Mercury [to Aeneas] said: You are now the husband of the highest of Karthage, you are laying foundations and building a beautiful city, you have forgotten your kingdom and your duties. The king of Olympus himself has sent me, commanding me to take this same command to you: What are you thinking? or for what gain are you delaying in Libya? If such a glorious future does not move you then remember your son Ascanius to whom the kingdom of Italy is promised.

Heu, quid agat? quibus nunc verbis audeat reginam adire furentem? unde ordiatur? Ita animum dubium nunc huc nunc illuc in varias partes versat. - what is he to do? or with what words should he now dare approach the furious queen? how should he begin? In this way he turns his vacillating [or maybe "uncertain" - dubium] mind now this way now that to various alternatives.

Is the point here that Aeneas is unable to deceive Dido about his flight from Karthage because she is in love?

Yes. She could sense that he was deceiving her because she was in love.